This invention relates to the field of process control and more particularly to a low-cost process controller having high accuracy analog to digital and digital to analog signal conversion. Prior art digitally driven industrial process controllers have employed commercially available 8-bit microprocessors interfaced to 8-bit peripheral equipment. More recently, 16-bit microprocessors have become available, but 8-bit peripheral equipment has continued to remain the low cost standard.
In typical prior art process control systems analog process measurement signals have been applied to 8-bit analog to digital signal converters which have generated process status information into 8-bit bytes for application to an 8-bit data bus servicing an appropriately selected microprocessor. The status information has been processed by the microprocessor in either 16-bit or 8-bit format for generation of appropriate process control signals. The process control signals have then been placed on the 8-bit data bus and transmitted to an 8-bit digital to analog converter for conversion to analog form. Such an arrangement is limited to 8-bit control accuracy. While some reasonably economical 10-bit and 12-bit integrated circuits are now available for supporting process control applications, they afford only modest improvements in control accuracy. Thus, there exists a need to provide an economical process controller which is able to make full use of the computing power of a 16-bit microprocessor.